\section{Discussion}

The $A5/1$ and $A5/2$ is yet another example why publishing the a encryption
algorithms is a must! Relying on the fact that people do not know how the
encryption scheme works is a foolish thing to do, since it has been proven time
and time again, that people have the resources and motivation to do reverse
engineering. 

Is the security still an issue, as the $A5/2$ cipher has been phases out since
2006? - Yes, as long as the protocol is still flawed!

Fixing the protocol flaws mentioned throughout this paper would probably require
the implementation of a whole new security protocol.
Implementing a new security protocol on the hardware level would be very
expensive, due to the magnitude of the already established GSM network. What
could be done instead is to move the security responsibility from the low level
of the protocol up to the application level. If this is done, a broken key in
the GSM protocol would just result in a plaintext that should look like random
bits, since the plaintext in the GSM protocol is the ciphertext of the
application level encryption.

A downside to have security on this level would be that it does take longer to
encrypt and decrypt compared to the these operations on the hardware level. But
with software capabilities of newer smart-phones this should not be a problem.
